The present invention relates generally to positive displacement pumps, and more particularly, to an improved "valveless" positive displacement pump of the type wherein the pumping action results from a combination of rotating and reciprocating action of a relieved piston within a ported cylinder. Because of the positive displacement action available with such kinds of pumps, they are capable of extremely high precision and are used in a wide variety of applications. Certain of these applications range from supplying ink to enormous printing presses of the type used to print daily newspapers to other applications, which include dispensing products that must be mixed with precision, including pharmaceuticals, chemical products of all kinds, and other liquids.
In general, pumps embodying the concept of a rod-type, relieved piston that reciprocates and rotates within a cylinder are well known. In the basic form, such an arrangement includes two basic parts, including a cylinder having inlet and outlet ports or passages, a rod-like piston that both rotates and reciprocates within the cylinder, and a relief extending chordwise across one end part of the piston so as to form a flat providing a part of a flow passage for liquid to be drawn into and expelled from a closed end pumping chamber.
In operation, the other or remote end of the rod on which the piston is formed includes a connecting rod or pin, one end of which extends radially outwardly from the piston remote end and the other end of which is journaled for universal movement, typically by a rod end or spherical bearing, within an offset leg on a portion of a rotary mechanism. In a typical construction, the rotary or driving mechanism is a crankshaft extending from the armature of an electric motor or the equivalent. This crank mechanism includes a shaft section concentric with the motor, an offsetting cheek or flange and a drive leg extending parallel to the shaft section and typically containing a spherical bearing. In such mechanisms, when the rotational axis of the piston and cylinder are inclined with respect to the rotational axis of the driving element, then the spherical bearing portion of the crank just referred to, upon rotation, will trace a circle in respect to the axis of its own shaft, but will trace an ellipse with respect to the axis of the driven element.
Consequently, the outer diameter end of the connecting rod or pin journalled in the spherical bearing will move through a path which oscillates axially with respect to the axis of the piston or driven element. The total axial excursion is the piston stroke. Pumps of this sort are shown, for example, in U.S. Pat. Nos. 3,168,872, 4,008,003, and 5,020,980.
While pumps of the type illustrated in this application have a number of advantages, including the ability to be tightly sealed, to create substantial static pressures and consequently to deliver very accurately metered quantities of liquid, one significant drawback to such pumps is that, with respect to any one particular pump, the instantaneous output of the pump varies throughout the operating cycle. In one-half of the operating cycle, there is no output, and in other portions, it varies depending on the crank angle. Thus, representing the operation of a typical pump as a sine wave laid out on a horizontal axis, the first 180.degree. or positive half wave form of a trace would represent pump output with respect to crank angle, while the second or negative 180.degree. portion of the sine wave would represent liquid taken in. Thus, it is clear that during one half of its operating cycle, the pump is delivering liquid and on an alternate part of the cycle, the pump is drawing liquid in. Consequently, driven at a constant speed, such a liquid pump not only has an oscillating or pulsating output, but also has no output half the time.
In the past, it has been suggested to overcome this drawback in two ways, neither of which has proven entirely satisfactory. One suggested method has been simply to arrange two pumps in substantially back-to-back relation, one on either side of a motor, placing their crankshafts in a 180.degree., out-of-phase relationship. Thus, while one piston and cylinder delivers liquid in one portion of its operating cycle, the other pump is drawing liquid in and when the first pump begins to draw in liquid, the second pump would displace or pump liquid out. This arrangement has disadvantages of higher costs and taking up more space. It requires that the liquid handling arrangements, such as porting and manifolding, for example, be doubled. In effect, it is no better than simply having two pump and motor arrangements operated together.
Another approach that has been taken is to have a single, double ended piston, provided with two reliefs, one on each end of the piston, and providing intake and exhaust ports for each one. According to this arrangement, a movement in one direction of the piston would displace liquid and at the same time draw liquid into the other end of the arrangement, in a manner partly analogous to the operation of a two-stroke cycle internal combustion engine.
However, there are significant drawbacks associated with this concept, the main difficulties being the need to provide the second piston with an extension or rod to equalize volume changes per degree of stroke on each end of the piston. This creates space problems and also creates very significant difficulties with sealing the components. One advantage of liquid pumps of this type in the first place is that they run in the presence of a liquid which is usually non-abrasive, and accordingly can use very tight but low friction seals. With the double ended arrangement discussed above, auxiliary seals such as rod wiper seals, O-rings, or the like are needed. This need to introduce auxiliary seals is a serious drawback in the prior art approach just discussed.
Consequently, there has been a need for an improved positive displacement pump of the above type wherein the advantages of a full wave operating cycle could be achieved in a manner which would not require excessive space or unduly large components, which would not require duplication of most of the elements of the drive mechanism and which, furthermore, would not require complex, unwieldy seal mechanisms.
In view of the failure of the prior art to provide a pump having certain of the foregoing advantages and characteristics, it is an object of the present invention to provide an improved positive displacement fluid pump.
Another object of the present invention is to provide a positive displacement fluid pump that will provide a substantially uninterrupted flow of liquid and requires operation only by a single crank mechanism.
A further object of the invention is to provide an improved positive displacement liquid pump able to be driven by a single driving element and yet providing liquid flow during all portions of its operating cycle.
A still further object of the invention is to provide an improved liquid pump that is simple in operation and very compact relative to prior known pumps.
Yet another object of the invention is to provide a positive displacement liquid pump with two pistons, and wherein a portion of one of the pump pistons also serves as a cylinder, and locates a second piston, with both pistons and cylinders being concentrically arranged.
Another object of the invention is to provide a positive displacement fluid pump or motor wherein each of a pair of pistons includes a connecting rod fixed to a piston end and wherein the drive mechanism includes a yoke arrangement with a bearing carded by each opposed leg of a single crank mechanism.
A further object of the invention is to provide a pump and pump drive arrangement which includes a pair of concentrically arranged pistons, one being solid and the other one being hollow, with the solid piston moving within the cylinder formed as a part of the hollow piston.
A still further object of the invention is to provide a positive displacement motor and drive arrangement wherein the pump includes concentrically arranged pistons and cylinders and the drive mechanism includes a rotary shaft portion and a yoke including parallel, spaced apart legs each carrying a bearing journalling an end of a connecting rod extending radially from an associated piston.
Yet another object of the invention is to provide a pump assembly having operating characteristics of two pumps but being formed in a single mechanism and able to be driven by a improved control system which includes a stepping motor arrangement.
Another object of the invention is to provide a pumping arrangement for supplying ink to large printing presses, said arrangement comprising a page pack including a housing receiving the improved ink, plural drive motors mounted on the housing, and appropriate manifolding arranged to permit continuous ink flow from the pumps during their operating cycles.
The foregoing and other objects and advantages of the invention are achieved in practice by providing a compact pump mechanism that includes an outer cylinder sleeve with two inlet and two outlet ports or passages, a combination piston and cylinder received within the outer sleeve and a piston received within the inner cylinder, with the piston and cylinder unit including a pair of chordwise reliefs and the inner cylinder a passage connecting one relief to its interior, and with each of the pistons including a remote end adapted to be journaled for rotation by a drive mechanism normally operated at an axis inclined to the rotational axis of the pistons in the pump unit.
The exact manner in which the foregoing and other objects and advantages of the invention are achieved in practice will become more clearly apparent when reference is made to the following detailed description of the preferred embodiment of the invention set forth by way of example and shown in the accompanying drawings, in which like reference numbers indicate corresponding parts throughout.